It is generally known to provide a power drive system for driving a sliding door in movement between an open position and a closed position, where the drive arrangement accommodates shifting between manual operation and positively driven powered operation of the door at any position along its path of movement while providing a control responsive to an overload to stop door movement in the event an object is trapped by the closing door. These types of power drive systems are especially well adapted for use in operating the sliding door of a van-type vehicle. Typically, a power drive system is capable of driving an output member coupled to the door to drive the door in either direction over a relatively long working stroke. The coupling between the output member and the door can take the form of a positive mechanical interconnection between the motor and the door operable in either direction of movement as required. Additional problems may be presented where the power drive system is to power the sliding door of a van-type vehicle over and above the foregoing considerations applicable to sliding doors in general.
The power drive system for a sliding door in a van-type vehicle application is conventionally mounted on either longitudinally extending side of the van and the system may be operated by control switches accessible from the driver's seat. However, there are many occasions where the driver may desire to open or close the door manually, such as when the driver is outside the van loading or unloading articles through the sliding door and the controls are out of reach. A positively mechanically linked connection between the door and the power source will interfere with manual operation of the door and may disturb a relationship between the door and drive relied on by the control system to sense the position of the door along its path of travel.
Translation of a vehicle door requires an efficient set of machine elements and clutches to allow the door to overhaul the system. Yet the driving system must drive efficiently and not offer a significant resistance when being overhauled. A soft coupling may be employed to assure system loads remain in the range of acceptable machine element loads. A ball nut is a highly efficient machine element when used with a ball screw. However, the ball screw is rigid and expensive when used in applications requiring significant travel, while generally being incapable of accommodating movement along any path that is not linear.